@Mark1360
AirBnB are simply a booking platform - she is correct technically in taking you to court. I'm making no judgement as to whether she is right or wrong in her claim.
First she may be using this as a 'threat' to get a refund. You should reply and give a clear rebuttal of her claims - but do say anything other that a factual rebuttal. She may just go away if you respond factually to each of her claims.
If it does go to court then you will have to be prepared to provide your view and any evidence you can that shows her claim to be untrue. Small claims and sitting judges are quite broad in their intrepretation of the law and accompanying claim. So, for example, if she can prove it was misrepresented in some way on AirBnB, then she will probably win and the judge won't even ask her to prove it was unclean. If you can prove it was not misrepresented then that is a big plus as it's harder for the judge to believe her other statements.
Even if she wins there is a question as to how much she should get. AirBnB has a well documented process for helping guests who find property unsuitable: contact AirBnB immediatel (not 4 days after arriving in the property and staying there) and they will find alternative accommodation for you. If she chose not to do that, then the judge may find that she is only entitled to the amount she paid you (excluding any booking fee - which is what she paid AirBnB to find her accommodation).
At the end of the day it's a game of cat and mouse - even if she brings a claim, she may chicken out on the day and not turn up. You also need to think about how much stress you want. So, if you said, I am giving you 50% (without acknowleding any fault on your side) would she accept that? Perhaps...
Good luck!